Absolute position detection encoder

Abstract

An absolute position detection encoder includes a coder having a track provided with first graduations of an absolute pattern and second graduations of an incremental pattern, plural sensors movable relative to the coder along the longitudinal direction of the track, and a signal processing circuit for processing detection pulse trains, obtained upon reading the first graduations by the sensors, in synchronism with the time point corresponding to approximately the mid position of the minimum reading unit of the first graduation. The encoder outputs the relative position between the coder and the sensors in the form of parallel code signals as the absolute position read out from the absolute pattern graduations on the coder. By detecting the absolute pattern in synchronism with the time point corresponding to substantially the middle of the minimum reading unit of the first graduations, an absolute position detection signal of the correct code contents free of readout errors may be taken out for both the forward and reverse directions of the relative movement. On account of the signal selection function by the binary repetitive rectangular signal obtained from the incremental pattern reading results, the absolute position detection signal of the correct code contents may be taken out simultaneously with turn-on of the power source. The binary repetitive rectangular signal may also be used for generating a sub-scale signal for substantially improving the resolving power.